Optical fiber communication systems frequently comprise one or more switches that can change the optical path, e.g., to select transmission lines. Most prior art optical fiber switches contain moving parts, and consequently are relatively slow and mechanically complex. See, for instance, Y. Ohmori et al., Applied Optics, Vol. 17 (22), p. 3531 (1978).
These drawbacks are largely overcome by non-mechanical switches such as the magneto-optical switch of M. Shirasaki et al., Applied Optics, Vol. 23 (19), p. 3271 (1984). The prior art switch comprises a 45.degree. Faraday rotator consisting of a thin YIG (yttrium iron garnet) plate and an electromagnet with a core of semihard magnetic material. As can be seen from FIG. 4 of the Shirasaki reference, the core is a gapped annular ring, with the YIG plate disposed in the gap. This configuration has some disadvantages. Among the disadvantages are bulkiness, relatively complicated shaping of the magnet core, and relatively high profile.
In view of the importance of non-mechanical optical fiber switches for optical fiber communication systems and other applications, it would be highly desirable to have available a more robust switch of more convenient geometry. This application discloses such a switch.
A commercially available optical isolator comprises a permanent magnet (SmCo) with a square or rectangular cross section axial bore. A YIG member is sandwiched between two rutile wedges, and the combination is inserted into the bore of the magnet. See FIG. 1 for a schematic representation of the prior art isolator. As is understood by those skilled in the art, an optical isolator is not a switch but is a non-reciprocal clement that transmits radiation in one direction only.